Abstract:

A power transmission switching device includes a power shaft that is
rotationally driven, a power transmission unit that is displaced between
first and second positions positioned in an axial direction of the power
shaft, a first positioning member that positions the power transmission
unit in the first position, and a second positioning member that
positions the power transmission unit in the second position. Any one or
both of the switching of the connection and non-connection between the
power shaft and the power transmission unit and the switching of the
connection and non-connection between the power transmission unit and a
driven part using the power shaft as a power source are performed by the
switching of the position of the power transmission unit. The power
transmission unit has at least one middle position between the first and
second positions, and is held in the middle position by a holding unit.

Claims:

1. A power transmission switching device comprising:a power shaft that is
rotationally driven;a power transmission unit that is displaced between
first and second positions positioned in an axial direction of the power
shaft;a first positioning member that positions the power transmission
unit in the first position; anda second positioning member that positions
the power transmission unit in the second position,wherein any one or
both of the switching of the connection and non-connection between the
power shaft and the power transmission unit and the switching of the
connection and non-connection between the power transmission unit and a
driven part using the power shaft as a power source are performed by the
switching of the position of the power transmission unit, andthe power
transmission unit has at least one middle position between the first and
second positions, in the middle position the power transmission unit is
held by a holding unit, independently of the first and second positioning
members.

2. A power transmission switching device comprising:a power shaft that is
rotationally driven;a power transmission unit that is provided so as to
be displaced between first and second positions positioned in an axial
direction of the power shaft, and transmits rotational torque of the
power shaft to a driven part using the power shaft as a power source;a
first positioning member that displaces the power transmission unit from
the second position toward the first position by pushing the power
transmission unit toward the first position, and positions the power
transmission unit in the first position; anda second positioning member
that is displaced in the axial direction of the power shaft, is engaged
with the power transmission unit, displaces the power transmission unit
from the first position toward the second position against a pushing
force of the first positioning member, and positions the power
transmission unit in the second position by holding the position of the
power transmission unit in the axial direction,wherein any one or both of
the switching of the connection and non-connection between the power
shaft and the power transmission unit and the switching of the connection
and non-connection between the power transmission unit and the driven
part are performed by the switching of the position of the power
transmission unit, andthe power transmission unit has at least one middle
position between the first and second positions, in the middle position
the power transmission unit is held against a pushing force of the first
positioning member by a holding unit, independently of the second
positioning member.

3. The power transmission switching device according to claim 1,wherein
the middle position of the power transmission unit is a non-connection
position where the power transmission unit is not connected to the power
shaft.

4. The power transmission switching device according to claim 1, further
comprising:a plurality of the driven parts that includes input gears
disposed on the circumference of a circle having an axis of the power
shaft as a center, respectively,wherein the power transmission unit
includes:an arm member that includes a shaft hole into which the power
shaft is inserted, is slidably displaced through the shaft hole in the
axial direction of the power shaft, and is swung about the power shaft,
the swing of the arm member being restrained by a restraining unit when
the power transmission unit is in the first position, and the restraint
caused by the restraining unit being released when the power transmission
unit is in the second position;a transmission gear that is provided to
the arm member, is engaged with one input gear of the plurality of input
gears and transmits rotational torque of the power shaft to the input
gear when the power transmission unit is in the first position, is
positioned at a completely different position where the transmission gear
is not engaged with the input gears when the power transmission unit is
in the second position, and is positioned at a position where the
transmission gear is connected to one input gear of the plurality of
input gears through the swing of the arm member; anda clutch unit that is
disengaged from the arm member when the power transmission unit is in the
first position, is engaged with the arm member and transmits the
rotational torque of the power shaft to the arm member when the power
transmission unit is in the second position, and swings the arm member.

5. The power transmission switching device according to claim 4,wherein
the clutch unit includes:power shaft side comb-toothed parts that are
provided at the power shaft and are rotated together with the power shaft
as a single body; andarm side comb-toothed parts that are provided at the
arm member, are separated from the power shaft side comb-toothed parts
when the power transmission unit is in the first position, and are
engaged with the power shaft side comb-toothed parts when the power
transmission unit is in the second position,in the power transmission
unit, the engaged part to be engaged with the second positioning member
is formed at a member separate from the arm member, and an elastic member
is provided between the engaged part and the arm member,when the engaged
part receives a force from the second positioning member and is displaced
from the first position toward the second position, the arm member is
displaced by an elastic force of the elastic member, andwhen the power
transmission unit is in the second position, the arm side comb-toothed
parts are pressed against the power shaft side comb-toothed parts by the
elastic force of the elastic member.

6. The power transmission switching device according to claim 5,wherein
each of faces of teeth of the power shaft side comb-toothed parts and the
arm side comb-toothed parts, which come in contact with each other, forms
a predetermined angle with respect to the axial direction of the power
shaft, andthe elastic force of the elastic member is larger than a
component, which is parallel to the axial direction, of pressure, which
is generated on the faces of the teeth when the power shaft side
comb-toothed parts transmit rotational torque to the arm side
comb-toothed parts, so that the arm side comb-toothed parts and the power
shaft side comb-toothed parts are pressed against each other and
maintained.

7. The power transmission switching device according to claim 5,wherein
the shaft hole of the arm member into which the power shaft is inserted
is formed by a sleeve that forms a cylindrical shape,the engaged part is
formed at a case member that includes the arm side comb-toothed parts and
the power shaft side comb-toothed parts therein,the case member includes
openings at both ends thereof in the axial direction of the power shaft,
one opening of the case member is formed so that a predetermined gap is
formed between an outer peripheral surface of the sleeve and itself, and
the other opening is formed so as to come in sliding contact with the
outer peripheral surface of the power shaft,the power shaft side
comb-toothed parts are formed at a cylindrical member that includes a
flange coming in sliding contact with an inner peripheral surface of the
case member, andmoment, which is generated at the case member when the
second positioning member presses the engaged part, is taken by a contact
portion between the power shaft and the opening of the case member, and a
contact portion between the inner peripheral surface of the case member
and the flange of the cylindrical member.

8. The power transmission switching device according to claim 4,wherein
while the power transmission unit returns to the first position before
being displaced from the first position toward the middle position and
then displaced to the second position, the restraining unit restrains the
swing of the arm member.

9. The power transmission switching device according to claim 4,wherein
the arm member is in any one state of a state where the swing of the arm
member is restrained by at least the restraining unit and a state where
rotational torque of the power shaft is transmitted by the clutch unit,
in the entire displacement area when being slidably displaced in the
axial direction of the power shaft.

10. The power transmission switching device according to claim 1,wherein
the holding unit, which holds the power transmission unit in the middle
position, includes:a restrained portion that is provided at the power
transmission unit, anda cam member that includes a guide passage guiding
the restrained portion during the displacement of the power transmission
unit, and a stopper that regulates the displacement of the restrained
portion toward the first position and is formed on the guide passage.

11. A recording apparatus comprising:a recording head that performs
recording on a medium to be recorded;a carriage that is provided with the
recording head and is moved in a scanning direction of the recording
head; anda power transmission switching device according to claim
1,wherein the carriage forms the second positioning member.

Description:

BACKGROUND

[0001]1. Technical Field

[0002]The present invention relates to a power transmission switching
device that switches the transmission and non-transmission of rotational
torque from a power shaft rotationally driven by a motor or the like to a
driven part using the power shaft as a driving source. Further, the
present invention relates to a recording apparatus that is provided with
the power transmission switching device.

[0003]2. Related Art

[0004]An ink jet printer, which is an example of a recording apparatus,
will be exemplified below. The ink jet printer includes a plurality of
objects to be driven, such as a feeding device that feeds a paper sheet,
a roller that transports the paper sheet, a carriage on which a recording
head is mounted, and a pump device that sucks ink from the recording
head. However, if a dedicated drive motor is provided to each of the
objects to be driven, cost is significantly increased. Accordingly, a
switching mechanism, which selectively switches the object driven by the
motor, is provided in order to drive the plurality of objects by one
motor.

[0005]The switching mechanism switches the object to be driven by the
switching of a gear train, and a carriage disclosed in JP-A-11-227179 or
JP-A-2001-162887 is used for the switching of the gear train.

[0006]According to the switching mechanism in the related art, if a
carriage is moved to the switching mechanism (home area), the switching
mechanism is unlocked, so that the switching of the object to be driven
can be performed. If the carriage is moved to the switching mechanism
returns to a printing area from the switching mechanism (home area) the
switching mechanism is locked. Accordingly, a state where power is
transmitted to a specific object to be driven is fixed.

[0007]Meanwhile, if a rotating shaft of a transport roller transporting a
paper sheet is used as a power shaft and power is transmitted to a
switching mechanism from the power shaft, power is not transmitted to the
objects to be driven (for example, a feeding device and the like) and
only the power shaft (transport roller) may be intended to be rotated
like, for example, when a paper jam is treated.

[0008]However, according to the switching mechanism in the related art,
the carriage needs to be always held at the switching mechanism (home
area) not to transmit power to the object to be driven. Accordingly,
degree of freedom deteriorates in the operation of a carriage.

SUMMARY

[0009]An advantage of some aspects of the invention is to provide a
switching mechanism that can be maintained in a specific state without
deterioration of the degree of freedom in the operation of a carriage,
and particularly, can be maintained in several states independently of a
carriage.

[0010]According to a first aspect of the invention, a power transmission
switching device includes a power shaft that is rotationally driven, a
power transmission unit that is displaced between first and second
positions positioned in an axial direction of the power shaft, a first
positioning member that positions the power transmission unit in the
first position, and a second positioning member that positions the power
transmission unit in the second position. Any one or both of the
switching of the connection and non-connection between the power shaft
and the power transmission unit and the switching of the connection and
non-connection between the power transmission unit and a driven part
using the power shaft as a power source are performed by the switching of
the position of the power transmission unit. The power transmission unit
has at least one middle position between the first and second positions,
in the middle position the power transmission unit is held by a holding
unit, independently of the first and second positioning members.

[0011]According to this aspect, the power transmission unit, which
transmits rotational torque to the driven part from the power shaft, has
the first position where the power transmission unit is positioned by the
first positioning member, the second position where the power
transmission unit is positioned by the second positioning member, and
additionally, at least one middle position where the power transmission
unit can be held independently of the first and second positioning
members. Accordingly, when the first or second positioning member is also
used as another component, it may be possible to secure the degree of
freedom in the operation of the component by using the middle position.

[0012]According to a second aspect of the invention, a power transmission
switching device includes a power shaft, a power transmission unit, a
first positioning member, and a second positioning member. The power
shaft is rotationally driven. The power transmission unit is provided so
as to be displaced between first and second positions positioned in an
axial direction of the power shaft, and transmits rotational torque of
the power shaft to a driven part using the power shaft as a power source.
The first positioning member displaces the power transmission unit from
the second position toward the first position by pushing the power
transmission unit toward the first position, and positions the power
transmission unit in the first position. The second positioning member is
displaced in the axial direction of the power shaft, is engaged with the
power transmission unit, displaces the power transmission unit from the
first position toward the second position against a pushing force of the
first positioning member, and positions the power transmission unit in
the second position by holding the position of the power transmission
unit in the axial direction. Any one or both of the switching of the
connection and non-connection between the power shaft and the power
transmission unit and the switching of the connection and non-connection
between the power transmission unit and the driven part are performed by
the switching of the position of the power transmission unit. The power
transmission unit has at least one middle position between the first and
second positions, in the middle position the power transmission unit is
held against a pushing force of the first positioning member by a holding
unit, independently of the second positioning member.

[0013]According to this aspect, the power transmission unit, which
transmits rotational torque to the driven part from the power shaft, has
the first position where the power transmission unit is positioned by the
first positioning member, the second position where the power
transmission unit is positioned by the second positioning member, and at
least one middle position where the power transmission unit can be held
against a pushing force of the first positioning member independently of
the second positioning member. That is, the power transmission unit has
the first position and the middle position as positions that are held
even though the second positioning member is separated from the power
transmission unit.

[0014]Accordingly, it may be possible to secure the degree of freedom in
the operation of the second positioning member by using the middle
position. Further, it may be possible to quickly switch the position of
the power transmission unit to the middle position without performing
additional operations by only one action that displaces the power
transmission unit by the second positioning member.

[0015]According to a third aspect of the invention, in the power
transmission switching device according to the first or second aspect,
the middle position of the power transmission unit may be a
non-connection position where the power transmission unit is not
connected to the power shaft.

[0016]According to this aspect, the middle position of the power
transmission unit is a non-connection position where the power
transmission unit is not connected to the power shaft. Accordingly, it
may be possible to freely rotate the power shaft when the power
transmission unit is in the middle position.

[0017]According to a fourth aspect of the invention, the power
transmission switching device according to any one of the first to third
aspects may further include a plurality of the driven parts that includes
input gears disposed on the circumference of a circle having an axis of
the power shaft as a center, respectively. The power transmission unit
may include an arm member, a transmission gear, and a clutch unit. The
arm member includes a shaft hole into which the power shaft is inserted,
is slidably displaced through the shaft hole in the axial direction of
the power shaft, and is swung about the power shaft. The swing of the arm
member is restrained by a restraining unit when the power transmission
unit is in the first position, and the restraint caused by the
restraining unit is released when the power transmission unit is in the
second position. The transmission gear is provided to the arm member, is
engaged with one input gear of the plurality of input gears and transmits
rotational torque of the power shaft to the input gear when the power
transmission unit is in the first position, is positioned at a completely
different position where the transmission gear is not engaged with the
input gears when the power transmission unit is in the second position,
and is positioned at a position where the transmission gear is connected
to one input gear of the plurality of input gears through the swing of
the arm member. The clutch unit is disengaged from the arm member when
the power transmission unit is in the first position, is engaged with the
arm member and transmits the rotational torque of the power shaft to the
arm member when the power transmission unit is in the second position,
and swings the arm member.

[0018]According to this aspect, a plurality of driven parts is provided,
and one of the plurality of driven parts is selected through the swing of
the arm member. Accordingly, it may be possible to dispose the plurality
of driven parts (input gears) on the circumference of a circle, which has
the center of the swing of the arm member as a center. That is, it may be
possible to transmit rotational torque to the plurality of driven parts
by one driving shaft.

[0019]According to a fifth aspect of the invention, in the power
transmission switching device according to the fourth aspect, the clutch
unit may includes power shaft side comb-toothed parts that are provided
at the power shaft and are rotated together with the power shaft as a
single body; and arm side comb-toothed parts that are provided at the arm
member, are separated from the power shaft side comb-toothed parts when
the power transmission unit is in the first position, and are engaged
with the power shaft side comb-toothed parts when the power transmission
unit is in the second position. Further, in the power transmission unit,
the engaged part to be engaged with the second positioning member may be
formed at a member separate from the arm member, and an elastic member
may be provided between the engaged part and the arm member. When the
engaged part receives a force from the second positioning member and is
displaced from the first position toward the second position, the arm
member may be displaced by an elastic force of the elastic member. When
the power transmission unit is in the second position, the arm side
comb-toothed parts may be pressed against the power shaft side
comb-toothed parts by the elastic force of the elastic member.

[0020]The clutch unit, which transmits the rotational torque of the power
shaft to the arm member, includes power shaft side comb-toothed parts
that are rotated together with the power shaft as a single body, and arm
side comb-toothed parts that are formed at the arm member. When the
second positioning member displaces the arm member toward the second
position, the both comb-toothed parts are engaged with each other.
However, when the second positioning member displaces the arm member
toward the second position, there is a concern that the arm side
comb-toothed parts are not engaged with the power shaft side comb-toothed
parts and breakage occurs due to the collision between the ends of the
teeth of the both comb-toothed parts.

[0021]According to this aspect, in the power transmission unit, the
engaged part to be engaged with the second positioning member is formed
at a member separate from the arm member, and the arm member is displaced
by the elastic force of the elastic member that is provided between the
engaged part and the arm member. Accordingly, even though the arm side
comb-toothed parts are not engaged with the power shaft side comb-toothed
parts and the ends of the teeth of the both comb-toothed parts collide
with each other, only the arm member can be stopped in that position and
the breakage of the teeth may be prevented. In addition, since the arm
side comb-toothed parts are pushed so as to be engaged with the power
shaft side comb-toothed parts by the elastic force of the elastic member,
the both comb-toothed parts may be correctly engaged with each other if
the power shaft is rotated by a predetermined angle.

[0022]According to a sixth aspect of the invention, in the power
transmission switching device according to the fifth aspect, each of
faces of teeth of the power shaft side comb-toothed parts and the arm
side comb-toothed parts, which come in contact with each other, may form
a predetermined angle with respect to the axial direction of the power
shaft. The elastic force of the elastic member may be larger than a
component, which is parallel to the axial direction, of pressure, which
is generated on the faces of the teeth when the power shaft side
comb-toothed parts transmit rotational torque to the arm side
comb-toothed parts, so that the arm side comb-toothed parts and the power
shaft side comb-toothed parts are pressed against each other and
maintained.

[0023]If each of faces of teeth of the power shaft side comb-toothed parts
and the arm side comb-toothed parts, which come in contact with each
other, forms a predetermined angle with respect to the axial direction of
the power shaft, the arm side comb-toothed parts tend to be separated
from the power shaft side comb-toothed parts due to a component, which is
parallel to the axial direction, of pressure that is generated on the
faces of the teeth when the power shaft side comb-toothed parts transmit
rotational torque to the arm side comb-toothed parts. In this case, the
faces of the teeth slide each other, and the arm side comb-toothed parts,
that is, the arm member is unnecessarily swung. For this reason, there is
a concern that the positioning accuracy of the transmission gear
deteriorates. However, according to this aspect, the elastic force of the
elastic member is larger than the component parallel to the axial
direction. Accordingly, when the power shaft side comb-toothed parts
transmit rotational torque to the arm side comb-toothed parts, it may be
possible to prevent the arm member from being unnecessarily swung.

[0024]According to a seventh aspect of the invention, in the power
transmission switching device according to the fifth or sixth aspect, the
shaft hole of the arm member into which the power shaft is inserted may
be formed by a sleeve that forms a cylindrical shape, the engaged part
may be formed at a case member that includes the arm side comb-toothed
parts and the power shaft side comb-toothed parts therein, the case
member may include openings at both ends thereof in the axial direction
of the power shaft, one opening of the case member may be formed so that
a predetermined gap is formed between an outer peripheral surface of the
sleeve and itself, and the other opening may be formed so as to come in
sliding contact with the outer peripheral surface of the power shaft. The
power shaft side comb-toothed parts may be formed at a cylindrical member
that includes a flange coming in sliding contact with an inner peripheral
surface of the case member. The moment, which is generated at the case
member when the second positioning member presses the engaged part, may
be taken by a contact portion between the power shaft and the opening of
the case member, and a contact portion between the inner peripheral
surface of the case member and the flange of the cylindrical member.

[0025]As described in the fourth aspect, the engaged part to be engaged
with the second positioning member in the power transmission unit is
formed at a member separate from the arm member and the arm member is
displaced by the elastic force of the elastic member that is provided
between the engaged part and the arm member. Accordingly, even though the
arm side comb-toothed parts are not engaged with the power shaft side
comb-toothed parts and the teeth of the both comb-toothed parts collide
with each other, the arm member can be stopped at the position where the
ends of the teeth collide with each other and the breakage of the teeth
may be prevented.

[0026]In this case, the engaged part is pushed by the second positioning
member and is continuously displaced in the axial direction of the power
shaft. However, if the engaged part is pushed by the second positioning
member, moment may be generated at the case member. Accordingly, when the
cam member comes in contact with the arm member (sleeve), the case member
displaces the arm member. For this reason, there is a concern that the
ends of the teeth of the arm side comb-toothed parts and the power shaft
side comb-toothed parts come in strong contact with each other and are
broken. However, according to this aspect, the moment is taken by other
contact portions so that case member and the arm member do not come in
contact with each other. Therefore, it may be possible to prevent the
above-mentioned problem.

[0027]According to an eighth aspect of the invention, in the power
transmission switching device according to any one of the fourth to
seventh aspects, while the power transmission unit returns to the first
position before being displaced from the first position toward the middle
position and then displaced to the second position, the restraining unit
may restrain the swing of the arm member.

[0028]According to this aspect, the restraining unit, which restrains the
swing of the arm member when the power transmission unit is in the first
position where power is transmitted to the driven part, restrains the
swing of the arm member while the position of the power transmission unit
is switched to the first position, the middle position, and the first
position in this order. Accordingly, the transmission gear is maintained
while selecting any one of the plurality of input gears. As a result,
when the power transmission unit returns to the first position, the
selected driven part may be promptly driven without selecting one of the
input gears.

[0029]According to a ninth aspect of the invention, in the power
transmission switching device according to any one of the fourth to
eighth aspects, the arm member may be in any one state of a state where
the swing of the arm member is restrained by at least the restraining
unit and a state where rotational torque of the power shaft is
transmitted by the clutch unit, in the entire displacement area when
being slidably displaced in the axial direction of the power shaft.

[0030]According to this aspect, since the arm member is not free in the
entire displacement area between the first and second positions, it may
be possible to correctly control the attitude of the arm member without
the unintended swing of the arm member.

[0031]According to a tenth aspect of the invention, in the power
transmission switching device according to any one of the first to ninth
aspects, the holding unit, which holds the power transmission unit in the
middle position, may include a restrained portion and a cam member. The
restrained portion is provided at the power transmission unit. The cam
member includes a guide passage that guides the restrained portion during
the displacement of the power transmission unit, and a stopper that
regulates the displacement of the restrained portion toward the first
position and is formed on the guide passage.

[0032]According to this aspect, the holding unit, which holds the power
transmission unit in the middle position, includes a restrained portion
that is provided at the power transmission unit, and a cam member that is
engaged with the restrained portion. Accordingly, the structure of the
holding unit, which holds the power transmission unit in the middle
position, is simplified, so that it may be possible to make the holding
unit at low cost.

[0033]According to an eleventh aspect of the invention, a recording
apparatus includes a recording head that performs recording on a medium
to be recorded, a carriage that is provided with the recording head and
is moved in a scanning direction of the recording head, and a power
transmission switching device according to any one of the first to ninth
aspects. The carriage may form the second positioning member.

[0034]According to this aspect, it may be possible to obtain the same
advantages as any one of the first to ninth aspects from the recording
apparatus. Further, the carriage, which is an existing component of the
recording apparatus, forms the second positioning member that switches
the position of the power transmission unit from the first position to
the second position against the pushing force of the first positioning
member pushing the power transmission unit toward the first position.
Accordingly, since an existing component is used, it may be possible to
prevent the increase of manufacturing cost of the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]The invention will be described with reference to the accompanying
drawings, wherein like numbers reference like elements.

[0036]FIG. 1 is a side cross-sectional view showing a paper sheet
transport path of a printer according to an embodiment of the invention.

[0037]FIG. 2 shows a front view of a power transmission switching device
according to an embodiment of the invention and a block diagram of a
control system.

[0038]FIG. 3 is a perspective view of the entire power transmission
switching device according to the embodiment of the invention.

[0039]FIG. 4 is a perspective view of the entire power transmission
switching device according to the embodiment of the invention.

[0040]FIG. 5 is a perspective view of main parts of the power transmission
switching device according to the embodiment of the invention.

[0041]FIG. 6 is a perspective view of main parts of the power transmission
switching device according to the embodiment of the invention.

[0042]FIG. 7 is a perspective view of main parts of the power transmission
switching device according to the embodiment of the invention.

[0043]FIG. 8A is a perspective view of a case member, and FIG. 8B is a
perspective view of a cam member.

[0044]FIG. 9 is a cross-sectional view of the power transmission switching
device according to the embodiment of the invention.

[0045]FIG. 10 is a cross-sectional view of the power transmission
switching device according to the embodiment of the invention.

[0046]FIG. 11 is a cross-sectional view of the power transmission
switching device according to the embodiment of the invention.

[0047]FIG. 12 is a cross-sectional view of the power transmission
switching device according to the embodiment of the invention.

[0048]FIG. 13 is a cross-sectional view of the power transmission
switching device according to the embodiment of the invention.

[0049]FIG. 14 is a cross-sectional view of the power transmission
switching device according to the embodiment of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0050]An embodiment of the invention will be described below with
reference to FIGS. 1 to 14. FIG. 1 is a side cross-sectional view showing
a paper sheet transport path of an ink jet printer (hereinafter, referred
to as a "printer") 1 that is a recording apparatus according to an
embodiment of the invention. FIG. 2 shows a front view of a power
transmission switching device 50 according to an embodiment of the
invention and a block diagram of a control system. FIGS. 3 and 4 are
perspective views of the entire power transmission switching device 50
according to the embodiment of the invention. FIGS. 5 to 7 are
perspective views of main parts of the power transmission switching
device 50 according to the embodiment of the invention. FIG. 8A is a
perspective view of a case member 65, and FIG. 8B is a perspective view
of a cam member 71.

[0051]Further, FIGS. 9 to 13 are cross-sectional views of the power
transmission switching device 50 according to the embodiment of the
invention taken along a plane including the cam member 71, and show the
changes in operation. FIG. 14 is a cross-sectional view of the power
transmission switching device 50 according to the embodiment of the
invention taken along a plane including a carriage engaging part 65a.

1. Structure of Recording Apparatus

[0052]The entire structure of the printer 1 will be outlined below with
reference to FIGS. 1 and 2. The printer 1 includes a feeding device 2 at
the bottom thereof. The printer feeds paper sheets (generally cut sheets:
hereinafter, referred to as "paper sheets P"), which are examples of
"media to be recorded", from the feeding device 2 one by one, performs
recording (ink jet recording) by a recording device 4, and discharges the
paper sheets toward a paper discharge stacker (not shown) that is
provided at the front portion of the printer (on the left side in FIG.
1).

[0053]Components provided on a paper sheet transport path will be further
described in detail below. The feeding device 2 includes a paper sheet
cassette 11, a pickup roller 16, a guide roller 20, and a separation unit
21.

[0054]The paper sheet cassette 11, which can receive a plurality of paper
sheets P while the paper sheets are stacked, can be mounted on or
separated from a main body of the feeding device 2 at the front portion
of the printer. The pickup roller 16, which is rotationally driven by a
PF (paper feed) motor 9 (FIG. 2), is mounted on a swing member 17 that is
swung about a pivot 18. The pickup roller comes in contact with the paper
sheet received in the paper sheet cassette 11 and is rotated so as to
feed the uppermost paper sheet P from the paper sheet cassette 11.

[0055]A separation member 12 is provided at a position that faces the ends
of the paper sheets received in the paper sheet cassette 11, and the
uppermost paper sheet P is moved toward the downstream side while the
front end of the uppermost paper sheet P to be fed comes in sliding
contact with the separation member 12. Accordingly, a first separation
between the uppermost paper sheet and the next paper sheet P is
performed. A guide roller 20, which can be freely rotated, is provided on
the downstream side of the separation member 12. The separation unit 21,
which includes a separation roller 22 and a driving roller 23 and
performs a second separation of the paper sheet P, is provided on the
downstream side of the guide roller.

[0056]A first paper feed unit 25 is provided on the downstream side of the
separation unit 21. The first paper feed unit includes a driving roller
26 that is rotationally driven by the PF motor 9 (FIG. 2), and an assist
roller 27 that is rotated while the paper sheet P is nipped between
itself and the driving roller 26. The paper sheet P is further fed toward
the downstream side by the first paper feed unit 25. Meanwhile, reference
numeral 29 denotes a driven roller that reduces a paper-passing load
generated when the paper sheet P passes through a curving reversing path
(particularly, when the rear end of the paper sheet passes through the
curving reversing path).

[0057]A second paper feed unit 31 is provided on the downstream side of
the driven roller 29. The second paper feed unit includes a driving
roller 32 that is rotationally driven by the PF motor 9 (FIG. 2), and an
assist roller 33 that is rotated while the paper sheet P is nipped
between itself and the driving roller 32. The paper sheet P is further
fed toward the downstream side by the second paper feed unit 31.

[0058]The recording device 4 is disposed on the downstream side of the
second paper feed unit 31. The recording device 4 includes a transport
unit 5, a recording head 42, a front paper guide part 39, and a discharge
unit 6. The transport unit 5 includes a transport driving roller 35 that
is rotationally driven by the PF motor 9 (FIG. 2), and a transport driven
roller 36 that is journaled to an upper paper guide part 37 so as to be
pressed against the transport driving roller 35 and be rotated.
Accordingly, the paper sheet P is fed toward a position, which faces the
recording head 42, with high accuracy by the transport unit 5.

[0059]The recording head 42 is provided at the bottom of a carriage 40.
The carriage 40 is driven by a CR (carriage) motor 8 (FIG. 2) so as to
reciprocate in a main scanning direction while being guided by a guide
shaft 41 extending in the main scanning direction (in a direction
perpendicular to the plane of FIG. 1). Meanwhile, the carriage 40 is a
so-called off-carriage type where an ink carriage is not mounted. An ink
carriage (not shown) is provided independently of the carriage 40, and
ink is supplied to the recording head 42 from the ink carriage through an
ink supply tube (not shown).

[0060]A front paper guide part 39 is provided in the position that faces
the recording head 42, and a distance between the paper sheet P and the
recording head 42 is defined by the front paper guide part 39. Further, a
discharge unit 6 is provided on the downstream side of the front paper
guide part 39. The discharge unit includes a discharge driving roller 44
that is rotationally driven by the PF motor 9 (FIG. 2), and a discharge
driven roller 45 that is rotated while coming in contact with the
discharge driving roller 44. The paper sheet P on which recording has
been performed by the recording device 4 is discharged to a stacker (not
shown), which is provided at the front portion of the printer, by the
discharge unit 6. The entire structure of the printer 1 has been
described above.

2. Structure and Operation of Power Transmission Switching Device

[0061]Subsequently, the structure of the power transmission switching
device 50 will be described. First, the structure of the power
transmission switching device 50 will be outlined below with reference to
FIG. 2. As shown in FIG. 2, the printer 1 includes two motors as a power
source. One of the motors is the PF (paper feed) motor 9, and the other
thereof is the CR (carriage) motor 8. The two motors are controlled by a
controller 7.

[0062]The PF motor 9 is a common driving source of rollers, such as the
driving roller 35 (transport unit 5) the driving roller 44 (discharge
unit 6), and the driving roller 32 (second paper feed unit 31). The PF
motor drives various driven parts of the printer 1 requiring power, such
as the feeding device 2 and a pump device (not shown), by the power
transmission switching device 50. Meanwhile, mechanisms A to F shown in
FIG. 2 indicate the plurality of driven parts, and the mechanisms A to F
are appropriately and generally referred to as "driven parts" in the
following description.

[0063]However, the rollers provided on the paper sheet transport path,
such as the driving roller 35 (transport unit 5), the driving roller 44
(discharge unit 6), and the driving roller 32 (second paper feed unit
31), make a one-to-one connection with the PF motor 9 not through the
power transmission switching device. When the PF motor 9 is rotated, the
rollers are always rotated in accordance with the rotation of the PF
motor.

[0064]The power transmission switching device 50 uses the driving roller
35 as a power shaft, receives rotational torque from the driving roller
35, and transmits the rotational torque to the driven parts. Meanwhile,
reference numerals 59A to 59F denote input gears of the driven parts. For
example, when rotational torque is transmitted to the input gear 59A, the
mechanism A is operated.

[0065]The power transmission switching device 50 includes a power
transmission unit 54. The power transmission unit is provided so as to be
displaced (is provided so that positions can be switched) between first
and second positions that are positioned in an axial direction of the
driving roller 35, and transmits the rotational torque of the driving
roller 35 to the driven parts from the driving roller 35 in the first
position.

[0066]The power transmission unit 54 is provided with an arm member 55
including a sleeve 55c (see FIGS. 5 to 7 and FIGS. 9 to 13). The sleeve
forms a shaft hole into which the driving roller 35 is inserted. The arm
member 55 is provided to be slidably displaced in the axial direction of
the driving roller 35 through the sleeve 55c and to be swung about the
driving roller 35 as shown by reference character "a".

[0067]A first planetary gear 57 and a second planetary gear 58 as a
"transmission gear" are rotatably provided to the arm member 55. In this
case, the swing of the arm member 55 is restrained by a restraining unit
(to be described below) in the first position, but the arm member can be
swung about the driving roller 35 in the second position. If the arm
member is swung, the second planetary gear 58 is positioned at a position
where the second planetary gear can be engaged (connected) with any one
of the plurality of input gears 59A to 59F.

[0068]However, if the power transmission unit is in the second position,
the second planetary gear 58 is positioned at a completely different
position where the second planetary gear is not actually engaged with
each of the input gears 59A to 59F (see FIGS. 4 and 13). If the position
of the power transmission unit is switched from the second position to
the first position, the second planetary gear 58 is engaged with any one
of the input gears 59A to 59F.

[0069]FIGS. 5 and 9 show that the power transmission unit 54 is in the
first position. The driving roller 35 is provided with a driving gear 56
that is rotated together with the driving roller 35 as a single body.
Accordingly, when the power transmission unit is in the first position as
shown in FIG. 5, the first planetary gear 57 is engaged with the driving
gear 56. Therefore, when the power transmission unit is in the first
position, rotational torque is transmitted to the driving gear 56, the
first planetary gear 57, the second planetary gear 58, and any one of the
input gears 59A to 59F, in this order. That is, any one of the driven
parts is driven.

[0070]Meanwhile, the power transmission unit is held in the first position
by a coil spring 68 that is a first positioning member (pushing member)
pushing the arm member 55 toward the frame 51. In more detail, a stopper
63 is provided at an axial end 35a of the driving roller 35, and the arm
member 55 is pushed toward the frame 51, that is, to the left side in
FIG. 9 by a pushing force of the coil spring 68 that is provided between
the stopper 63 and a case member 65 (to be described below). Accordingly,
the arm member 55 is bumped against the frame 51 by the pushing force,
and the power transmission unit is held in the first position.

[0071]Further, when the arm member is in the first position, the swing of
the arm member 55 is restrained by the restraining unit. In more detail,
a hole 55b is formed at the arm member 55, and positioning pins 52A to
52F (also see FIGS. 3 and 4) protrude from the frame 51 toward the arm
member 55.

[0072]The positioning pins 52A to 52F correspond to the input gears 59A to
59F, respectively, and are positioned near the input gears, respectively.
For example, when the second planetary gear 58 provided to the arm member
55 is engaged with the input gear 52A, the positioning pin 52A is
inserted into the hole 55b of the arm member 55. Accordingly, the swing
of the arm member 55 is restrained, so that the engagement between the
second planetary gear 58 and the input gear 59A is maintained.

[0073]As described above, the hole 55b of the arm member 55 and the
positioning pins 52A to 52F form the restraining unit that restrains the
swing of the arm member 55. Meanwhile, each of the positioning pins 52A
to 52F is formed in a shape that is tapered toward the end. Accordingly,
even though being not aligned with the center of the hole 55b to some
extent, the front end of each of the positioning pin is correctly
inserted into the hole 55b.

[0074]Subsequently, a position switching member that switches the position
of the power transmission unit 54 formed as described above, and a clutch
unit 61 that swings the arm member 55 will be described. As shown in FIG.
5, arm side comb-toothed parts 55a are formed at the end of the sleeve
55c of the arm member 55 so that a plurality of protrusions (teeth)
protruding in the axial direction of the driving roller 35 is disposed in
a circumferential direction of the driving roller 35 at predetermined
intervals.

[0075]Further, an arm driving member (cylindrical member) 66 is provided
at a position that faces the arm side comb-toothed parts 55a, so as to be
rotated together with the driving roller 35 as a single body. Like the
arm side comb-toothed parts 55a, power shaft side comb-toothed parts 66a
are formed on the arm driving member 66 at a position facing the arm side
comb-toothed parts 55a so that a plurality of protrusions (teeth)
protruding in the axial direction of the driving roller 35 is disposed in
the circumferential direction of the driving roller 35 at predetermined
intervals.

[0076]When the power transmission unit 54 is in the second position, the
arm side comb-toothed parts 55a and the power shaft side comb-toothed
parts 66a are engaged with each other as shown in FIG. 7. When the power
transmission unit 54 is in the second position, the rotational torque of
the driving roller 35 is transmitted to the arm member 55 by the
engagement between the arm side comb-toothed parts and the power shaft
side comb-toothed parts. Accordingly, the driving roller 35 and the arm
member 55 are rotated (swung).

[0077]More specifically, a case member 65, which forms a cylindrical shape
so as to include the arm side comb-toothed parts 55a and the power shaft
side comb-toothed parts 66a therein as shown in FIGS. 5 and 14, is
provided. The case member is formed so that the sleeve 55c is inserted
into the case member 65 from one opening of the case member and a
predetermined gap is formed between the inner peripheral surface 65e of
the one opening and the outer peripheral surface of the sleeve 55c.
Further, the case member is formed so that the inner peripheral surface
65c (also see FIG. 8A) of the other opening of the case member comes in
sliding contact with the outer peripheral surface of the driving roller
35.

[0078]A coil spring 69 serving as a pushing member is provided between the
case member 65 and the arm member 55. If the case member 65 is displaced
to the right side in FIG. 14 against the pushing force of the coil spring
68, the arm member 55 is also displaced to the right side (from the first
position toward the second position) by a pushing force of the coil
spring 69.

[0079]In this case, the case member 65 and the arm member 55 are engaged
with each other with the coil spring 69 interposed therebetween.
Accordingly, even though the arm side comb-toothed parts 55a and the
power shaft side comb-toothed parts 66a are not correctly engaged with
each other and the ends of the teeth of the both comb-toothed parts
collide with each other, only the case member 65 can be displaced while
the arm member 55 (arm side comb-toothed parts 55a) is stopped by the
compression of the coil spring 69 as shown in FIG. 6.

[0080]Therefore, even though the arm side comb-toothed parts 55a and the
power shaft side comb-toothed parts 66a are not correctly engaged with
each other and the ends of the teeth of the both comb-toothed parts
collide with each other, breakage does not occur. If the driving roller
35 is rotated by a predetermined angle while the ends of the both
comb-toothed parts collide with each other, the arm side comb-toothed
parts 55a and the power shaft side comb-toothed parts 66a are correctly
engaged with each other as shown in FIG. 7.

[0081]Further, when the power transmission unit 54 is in the second
position, the arm side comb-toothed parts 55a and the power shaft side
comb-toothed parts 66a are engaged with each other as shown in FIGS. 7,
13, and 14. If the driving roller 35 is rotated in this state, the arm
member 55 is swung in accordance with the rotation of the driving roller
and the second planetary gear 58 is positioned at a position where the
second planetary gear is engaged with any one of the input gears 59A to
59F.

[0082]Meanwhile, the positioning is performed using a positioning frame 60
(FIG. 2). That is, when the arm member 55 is swung in a counterclockwise
direction of FIG. 2 and is bumped against the positioning frame 60 (that
is, when a drive current value of the PF motor 9 exceeds a threshold
value), the driving roller 35 is rotated by a predetermined angle, so
that the second planetary gear 58 is positioned at a target position.
Meanwhile, the rotation angle of the driving roller 35 may be detected by
a rotation detector (not shown).

[0083]The arm side comb-toothed parts 55a and the power shaft side
comb-toothed parts 66a form a clutch unit 61 that swings the arm member
55. When the power transmission unit 54 is in the first position, the
clutch unit is disengaged from the arm member 55 as described above. When
the power transmission unit 54 is in the second position, the clutch unit
is engaged with the arm member 55 and transmits the rotational torque of
the driving roller 35 to the arm member 55.

[0084]Subsequently, the switching of the position of the power
transmission unit 54 is performed by the coil spring 68 that pushes the
power transmission unit 54 toward the first position, and the carriage 40
that is a second positioning member (position switching member)
displacing the power transmission unit from the first position toward the
second position against the pushing force of the coil spring 68.

[0085]When the carriage 40 is in a recording area, that is, when the power
transmission unit 54 is not engaged with the carriage 40, the power
transmission unit 54 is maintained in the first position by the pushing
force of the coil spring 68 as described above. If the carriage 40 is
moved toward a home position (toward the axial end 35a of the driving
roller 35) in this state, the carriage engaging part 65a serving as an
engaged part formed at the case member 65 is engaged with the side
surface of the carriage 40.

[0086]Further, if the carriage 40 is further moved, the case member 65 is
pushed and the power transmission unit 54 is displaced from the first
position to the second position. As long as the carriage 40 is maintained
in the position, the power transmission unit 54 is held in the second
position. Meanwhile, since the arm side comb-toothed parts 55a are
pressed against the power shaft side comb-toothed parts 66a by the
pushing force of the coil spring 69 in this state, the engagement between
the both comb-toothed parts is maintained. Accordingly, the carriage 40
forms the second positioning member that displaces the power transmission
unit 54 from the first position to the second position and holds the
power transmission unit in the second position.

[0087]Subsequently, a middle position of the power transmission unit 54
will be described. As described above, the power transmission unit 54 is
displaced between the first position and the second position, rotational
torque is transmitted to the driven part from the driving roller 35 in
the first position, and the second planetary gear 58 is positioned by the
swing of the arm member 55 in the second position. A middle position is
set between the first position and the second position, and the power
transmission unit 54 can be held in the middle position against the
pushing force of the coil spring 68 by a holding unit 73 (to be described
below) independently of the carriage 40.

[0088]The middle position and the holding unit 73 that holds the power
transmission unit in the middle position will be described in detail
below.

[0089]As shown in FIG. 8A and 9, a restrained portion 65b is formed on the
case member 65 so as to have the shape of a protrusion that protrudes in
a lateral direction (a direction orthogonal to a displacement direction
of the case member 65). A cam member 71 is provided to a holder 70, which
is provided on the side of the case member 65, as shown in FIGS. 3 and 9.

[0090]The cam member 71 is provided to the holder 70 so as to be swingable
about a shaft 70a that extends in a direction orthogonal to the
displacement direction of the case member 65, and is pushed toward the
case member 65 by the coil spring 72.

[0091]The cam member 71 includes recesses in which the end of the
restrained portion 65b is received as shown in FIG. 8B, and a guide
passage that guides the end of the restrained portion 65b in a direction
indicated by an arrow of FIG. 8B in accordance with the displacement of
the case member 65. Further, a stopper 71b, which regulates the
displacement of the restrained portion 65b (case member 65) toward the
first position, is formed on the guide passage. The stopper is formed so
that the end of the restrained portion 65b cannot be moved in a direction
opposite to the guide direction indicated by the arrow (cannot return to
the first recess 71a) if being moved from a first recess 71a toward the
stopper 71b and getting over the stopper 71b.

[0092]The stopper 71b is disposed at a position where the return of the
case member 65 toward the first position is regulated when the case
member 65 (that is, the power transmission unit 54) is in the middle
position between the first and second positions. Accordingly, the power
transmission unit 54 can be held in the middle position against the
pushing force of the coil spring 68, independently of the carriage 40. As
described above, the restrained portion 65b and the cam member 71, which
are formed at the case member 65, form the holding unit 73 that holds the
power transmission unit 54 in the middle position.

[0093]The middle position will be further described below with reference
to FIGS. 9 to 13. FIG. 9 shows that the power transmission unit 54 is in
the first position. In this state, rotational torque is transmitted to
the driven part from the driving gear 56 of the driving roller 35 through
the first and second planetary gears 57 and 58 as described above.
Meanwhile, for convenience of description, FIGS. 9 to 13 show that
rotational torque is transmitted to the input gear 59A. Accordingly, the
input gears 59B to 59F and the positioning pins 52B to 52F, which should
be shown in drawings in principle, are omitted for simplification of the
drawings.

[0094]In this state, the restrained portion 65b is positioned in the first
recess 71a of the cam member 71. If the carriage 40 pushes the carriage
engaging part 65a of the case member 65 in this state and the power
transmission unit 54 is thus displaced to the right side in FIG. 9, the
restrained portion 65b gets over the stopper 71b of the cam member 71 and
is in a state where the return of the case member toward the first
position is regulated, that is, in a state where the power transmission
unit 54 is held in the middle position as shown in FIG. 10.

[0095]When the power transmission unit is in the middle position, the
driving gear 56 is disengaged from the first planetary gear 57 and the
second planetary gear 58 is also disengaged from the input gear 59A.
However, the arm side comb-toothed parts 55a and the power shaft side
comb-toothed parts 66a are not engaged with each other. Accordingly, when
the power transmission unit is in the middle position, rotational torque
is not transmitted to the driven part in accordance with the rotation of
the driving roller 35 and is also not transmitted to the arm member 55.
That is, the middle position of the power transmission unit 54 becomes a
non-connection position where the power transmission unit is not
connected to the driving roller 35.

[0096]Meanwhile, when the power transmission unit is in the middle
position, the positioning pin 52A is aligned with the hole 55b of the arm
member 55 and the positioning of the second planetary gear 58 is
maintained (the selection of the input gear 59A is maintained). Further,
when the power transmission unit returns to the first position before the
position of the power transmission unit is switched from the middle
position to the second position, the insertion of the positioning pin 52A
into the hole 55b of the arm member 55 is maintained, that is, the swing
of the arm member 55 is restrained.

[0097]Subsequently, if the carriage 40 is further moved toward the home
position, the end of the restrained portion 65b is moved to a second
recess 71c of the cam member 71 as shown in FIG. 11. Meanwhile, the
second recess 71c is formed to have a depth larger than the depth of the
stopper 71b. Accordingly, if being moved to the second recess 71c, the
end of the restrained portion 65b is not moved in a direction opposite to
the guide direction (arrow) shown in FIG. 8B and does not return to the
position where the end of the restrained portion is engaged with the
stopper 71b.

[0098]However, if the carriage 40 is separated toward the recording area
in this state, the end of the restrained portion 65b can be moved along a
locus indicated by an arrow of FIG. 8B (passing below a protrusion 71d)
and return to the first recess 71a. Before the position of the power
transmission unit is switched from the first position to the middle
position and then switched to the second position, the power transmission
unit 54 can return to the first position in this way.

[0099]Referring to FIG. 11, when the end of the restrained portion 65b is
moved to the second recess 71c of the cam member 71, the arm side
comb-toothed parts 55a and the power shaft side comb-toothed parts 66a
are not correctly engaged with each other and the ends of the teeth of
the both comb-toothed parts may collide with each other. However, only
the case member 65 can be moved to the right side in FIG. 11 as described
above and the driving roller 35 is then rotated by a predetermined angle,
so that the arm side comb-toothed parts 55a and the power shaft side
comb-toothed parts 66a can be correctly engaged with each other as shown
in FIGS. 12 and 13.

[0100]Meanwhile, when the positioning pin 52A begins to be not aligned
with the hole 55b of the arm member 55 as shown in FIG. 12, the arm side
comb-toothed parts 55a and the power shaft side comb-toothed parts 66a
already begin to be engaged with each other. That is, the arm member 55
is not free in the entire displacement area between the first and second
positions, and is necessarily in any one state of a state where the swing
of the arm member is restrained by the positioning pin 52A and a state
where the arm side comb-toothed parts 55a and the power shaft side
comb-toothed parts 66a are engaged with each other and rotational torque
may be transmitted from the driving roller 35.

[0101]Further, when the arm side comb-toothed parts 55a and the power
shaft side comb-toothed parts 66a are engaged with each other (are
pressed against each other), an elastic force of the coil spring 69
making the both comb-toothed parts be engaged with each other is set so
that the both comb-toothed parts are pressed against each other and
maintained. That is, in FIG. 14, each of the faces of the teeth of the
arm side comb-toothed parts 55a and the power shaft side comb-toothed
parts 66a, which come in contact with each other, forms a predetermined
angle with respect to the axial direction of the driving roller 35.
Accordingly, pressure F, which is generated on the faces of the teeth
when the power shaft side comb-toothed parts 66a transmit rotational
torque to the arm side comb-toothed parts 55a, may be decomposed into a
component f1 that is parallel to the axial direction of the driving
roller 35 and a component f2 that is orthogonal to the axial direction.

[0102]If the component f1 is large, the arm side comb-toothed parts 55a
are moved toward the left side in FIG. 14, that is, in a direction where
the arm side comb-toothed parts 55a are disengaged from the power shaft
side comb-toothed parts 66a, against the elastic force of the coil spring
69. In this case, the faces of the teeth of the arm side comb-toothed
parts 55a and the power shaft side comb-toothed parts 66a, which are
engaged with each other, slide each other. For this reason, the arm
member 55 is slightly swung. Accordingly, in order to prevent the arm
member from being slightly swung, the elastic force of the coil spring 69
is set to be larger than the force f1 so that the arm side comb-toothed
parts 55a and the power shaft side comb-toothed parts 66a are pressed
against each other and maintained.

[0103]Further, when the carriage 40 pushes the carriage engaging part 65a
to the right side in FIG. 14, clockwise moment in FIG. 14 is generated at
the case member 65. However, the moment is taken by a contact portion
between the driving roller 35 and the inner peripheral surface 65c of one
opening of the case member 65, and a contact portion between the inner
peripheral surface 65d of the case member 65 and a flange 66b of the arm
driving member 66. That is, the sleeve 55c of the arm member 55 does not
come in contact with the case member 65 due to the moment.

[0104]Subsequently, referring to FIG. 13, if the carriage 40 is moved
toward the recording area from the second position of the power
transmission unit 54 shown in FIG. 13 and is separated from the carriage
engaging part 65a, the power transmission unit 54 returns to the first
position by the pushing force of the coil spring 68. In this case, the
restrained portion 65b passes below the protrusion 71d of the cam member
71, that is, is moved in the guide direction indicated by the arrow of
FIG. 8B, and returns to the first recess 71a again.

[0105]The operation of the power transmission switching device 50 has been
described above.

3. Advantages of Power Transmission Switching Device

[0106]The advantages of the power transmission switching device 50 will be
described below.

[0107](1) The power transmission unit 54 has the first position where the
power transmission unit is held by the pushing force of the coil spring
68, the second position where the power transmission unit is held by the
carriage 40, and the middle position where the power transmission unit is
held by the holding unit 73 independently of the carriage 40. That is,
since not only the first position but also the middle position is set as
positions where the carriage 40 can be held without staying in the home
position, it may be possible to secure the degree of freedom in the
operation of the carriage 40.

[0108](2) It may be possible to quickly switch the position of the power
transmission unit 54 to the middle position without performing additional
operations by only one action that displaces the power transmission unit
54 from the first position to the middle position by the carriage 40.

[0109](3) Since the middle position of the power transmission unit 54 is a
non-connection position where the power transmission unit 54 is not
connected to the driving roller 35, it may be possible to secure free
rotation of the driving roller 35 when the power transmission unit 54 is
in the middle position.

[0110](4) The carriage engaging part 65a to be engaged with the carriage
40 is formed at the case member 65 that is a member separate from the arm
member 55. Accordingly, when the carriage engaging part 65a is pushed by
the carriage 40, the arm member 55 is displaced by the elastic force of
the coil spring 69 (elastic member) that is provided between the carriage
engaging part 65a (case member 65) and the arm member 55.

[0111]For this reason, even though the arm side comb-toothed parts 55a are
not engaged with the power shaft side comb-toothed parts 66a and the ends
of the teeth of the both comb-toothed parts collide with each other, the
arm member 55 can be stopped in that position and the breakage of the
teeth may be prevented. In addition, since the arm side comb-toothed
parts 55a are pushed so as to be engaged with the power shaft side
comb-toothed parts by the elastic force of the coil spring 69, the both
comb-toothed parts may be correctly engaged with each other if the
driving roller 35 is rotated by a predetermined angle.

[0112](5) When the arm side comb-toothed parts 55a and the power shaft
side comb-toothed parts 66a are engaged with each other, the elastic
force of the coil spring 69 making the both comb-toothed parts be engaged
with each other is set so that the arm side comb-toothed parts 55a and
the power shaft side comb-toothed parts 66a are pressed against each
other and maintained without being separated from each other.
Accordingly, the faces of the teeth of the arm side comb-toothed parts
55a and the power shaft side comb-toothed parts 66a, which are engaged
with each other, is prevented from sliding each other, which prevents the
arm member 55 from being slightly swung. Therefore, it may be possible to
prevent the deterioration of the positioning accuracy of the second
planetary gear 58 that is caused by the unintended swing of the arm
member 55.

[0113](6) The sleeve 55c of the arm member 55 does not come in contact
with the case member 65 due to the moment, which is generated at the case
member 65 when the carriage 40 pushes the carriage engaging part 65a.
Accordingly, while the teeth of the arm side comb-toothed parts 55a and
the power shaft side comb-toothed parts 66a are bumped against each
other, if the arm member 55 is further moved in a direction that makes
the arm side comb-toothed parts and the power shaft side comb-toothed
parts be engaged with each other, the teeth of the arm side comb-toothed
parts 55a and the power shaft side comb-toothed parts 66a come in strong
contact with each other. As a result, it may be possible to prevent the
breakage of the teeth.

[0114](7) While the power transmission unit 54 returns to the first
position before being displaced from the first position to the middle
position and then displaced to the second position, the swing of the arm
member 55 is restrained. Accordingly, the second planetary gear 58 is
maintained while selecting any one of the input gears 59A to 59F. As a
result, when the power transmission unit returns to the first position,
the selected driven part may be promptly driven without selecting one of
the input gears.

[0115](8) The arm member 55 is not free in the entire displacement area
between the first and second positions, and is necessarily in any one
state of a state where the swing of the arm member is restrained by the
positioning pins 52A to 52F and a state where the arm side comb-toothed
parts 55a and the power shaft side comb-toothed parts 66a are engaged
with each other and rotational torque may be transmitted from the driving
roller 35. Accordingly, it may be possible to correctly control the
attitude of the arm member 55 without the unintended swing of the arm
member 55.

[0116]Meanwhile, the structure where the power transmission switching
device according to the embodiment of the invention is applied to an ink
jet printer that is an example of the recording apparatus, and the
advantages thereof have been described above. However, the invention is
not limited thereto, and may be applied to other various apparatuses.